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SubjectRe: [PATCH] perf inject jit: Ignore memfd mmap events if jitdump present
On Tue, Aug 2, 2022 at 11:25 AM Brian Robbins
<brianrob@linux.microsoft.com> wrote:
>
> Some processes store jitted code in memfd mappings to avoid having rwx
> mappings. These processes map the code with a writeable mapping and a
> read-execute mapping. They write the code using the writeable mapping
> and then unmap the writeable mapping. All subsequent execution is
> through the read-execute mapping.
>
> perf inject --jit ignores //anon* mappings for each process where a
> jitdump is present because it expects to inject mmap events for each
> jitted code range, and said jitted code ranges will overlap with the
> //anon* mappings.
>
> Ignore /memfd: mappings so that jitted code contained in /memfd:
> mappings is treated the same way as jitted code contained in //anon*
> mappings.
>
> Signed-off-by: Brian Robbins <brianrob@linux.microsoft.com>

Acked-by: Ian Rogers <irogers@google.com>

> ---
> tools/perf/util/jitdump.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/tools/perf/util/jitdump.c b/tools/perf/util/jitdump.c
> index a23255773c60..335a3c61940b 100644
> --- a/tools/perf/util/jitdump.c
> +++ b/tools/perf/util/jitdump.c
> @@ -845,8 +845,12 @@ jit_process(struct perf_session *session,
> if (jit_detect(filename, pid, nsi)) {
> nsinfo__put(nsi);
>
> - // Strip //anon* mmaps if we processed a jitdump for this pid
> - if (jit_has_pid(machine, pid) && (strncmp(filename, "//anon", 6) == 0))
> + /*
> + * Strip //anon* and /memfd:* mmaps if we processed a jitdump for this pid
> + */
> + if (jit_has_pid(machine, pid) &&
> + ((strncmp(filename, "//anon", 6) == 0) ||
> + (strncmp(filename, "/memfd:", 7) == 0))

Related to this there is the prctl PR_SET_VMA_ANON_NAME which will
name mapping to start with "[anon:"
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/filesystems/proc.rst#n434
I wonder also we should be checking the pages are executable.

Thanks,
Ian

> return 1;
>
> return 0;
> --
> 2.25.1
>

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